1. Field of the Invention
The present invention relates to a resistance and a catalytic converter which are suitable for use in automotive exhaust emission control, and a method of operating such a catalytic converter.
2. Description of the Related Art
Catalytic converters for use in controlling automotive exhaust gas must have a predetermined temperature or above when operated so as to make its catalyst do catalytic action. Hence, the catalyst must be heated when the temperature thereof is not sufficiently high, i.e., at the beginning of running of a vehicle.
Such techniques for heating the catalyst have been proposed in, for example, Japanese Utility Model Laid-Open No. 67609/1988. This disclosed technique is a catalytic converter comprised of a main monolithic catalyst and a metal monolithic catalyst disposed upstream of and adjacent to the main ceramic monolithic catalyst. The metal monolithic catalyst comprises an electrically conductive metal substrate with alumina coated thereon.
However, in the catalytic converter disclosed in Japanese Utility Model Laid-Open No. 67609/1988, the metal monolithic catalyst, a preheater, disposed upstream and adjacent to the main monolithic catalyst comprises a foil-type metal honeycomb structure which is constructed such that a current is supplied from the inner periphery thereof to the outer periphery thereof to generate heat. The resistance of the metal monolithic catalyst is not adjusted (i.e., only the material, dimensions and rib thickness of the metal honeycomb structure as defined and no adjustment is made on the resistance of the metal honeycomb structure), and the metal monolithic catalyst thus exhibits insufficient temperature rising characteristics. Furthermore, since the electrodes are provided in the inner peripheral portion of the metal honeycomb structure, the central portion thereof does not act as a catalyst, and pressure loss is generated. Furthermore, the electrodes readily break due to the flow of exhaust gas.